One comes to believe whatever one repeats to oneself sufficiently often, whether the statement be true of false. It comes to be the dominating thought in one's mind.
There is no formula to it because writing every song, for me, is a little journey. The first note has to lift you and make you go, 'What's this?' You play C, but why is it that one day it leads to G and it didn't yesterday? I don't know. It's everything. It's the walk you take in the morning, it's the night before, the meeting with people, landscapes, the chats, all of that evolves in some way into melody, but I'm not sure how it's going to happen. I'm dealing with the unknown all the time and that is exciting.